Abstract: 【Aim】 To explore the toxicity of terpenoid compounds from Tithonia diversifolia against Spodoptera litura larvae and their effects on the activities of acetylcholinesterase (AChE) and detoxification enzymes, and to screen new active ingredients for the control of S. litura. 【Methods】 The stomach toxicity of three terpenoid compounds including squalene, caryophyllene oxide and α-pinene against Spodoptera litura larvae in 10 d was evaluated with laboratory bioassay by feeding the 3rd instar larvae with the diets supplemented with S-methoprene (positive control) and different concentrations of terpenoid compounds, respectively, and the larval weight was determined at 7 d after treatment. Enzyme-linked immunosorbnent assay was used to measure the effects of different concentrations of caryophyllene oxide on the activities of AChE and detoxification enzymes［carboxylesterase (CarE), cytochrome P450 (CYP450), and glutathione S-transferase (GST)］ in S. litura larvae after treatment for 3 d. Finally, molecular docking techniques were employed to simulate the binding affinity and binding sites of squalene, caryophyllene oxide and α-pinene with AChE, CarE, CYP450 and GST.【Results】 Within 3-5 d after the 3rd instar larvae of S. litura were fed with the diets supplemented with different concentrations of terpenoid compounds, 1×10^-1-1×10^-4 mg/mL caryophyllene oxide exhibited obvious toxicity to S. litura larvae, causing the corrected larval mortality rates significantly higher than squalene, α-pinene and the positive control. At 7 d after treatment, caryophyllene oxide significantly inhibited larval weight gain of S. litura, and the high-concentration caryophyllene oxide treatment group (1×10^－1 mg/mL) showed significantly lower larval weight than the positive control group. At 3 d after treatment with 1×10^-5-1×10^-3 mg/mL caryophyllene oxide, the activities of AChE, CarE and GST in S. litura larvae were significantly reduced, as compared with those in the positive control group, and the CYP450 activity was also significantly reduced as compared with that in the vehicle control (95% alcohol). Notably, when the test concentration of caryophyllene oxide was 1×10^－1 mg/mL, the AChE activity in S. litura larvae was negative. Molecular docking results further demonstrated that caryophyllene oxide had the strongest binding affinity to AChE, with the binding free energy lower than its interactions with CarE, CYP450 and GST. 【Conclusion】 Caryophyllene oxide exhibits high toxicity against S. litura larvae. It exerts insecticidal effects on S. litura by inhibiting AChE activity, highlighting its potential as a green control resource. This provides novel insights for the development and utilization of terpenoid compounds from T. diversifolia.

Key words: podoptera litura, squalene, caryophyllene oxide, α-pinene, molecular docking, acetylcholinesterase, detoxification enzymes